The present invention relates to heating, ventilation, and air conditioning (“HVAC”) systems, and more particularly to HVAC control systems.
Users typically expect a thermostat for a heating, ventilation, and air conditioning (HVAC) system to keep a controlled temperature within 1° F. (0.5° C.) of a temperature set point. Typically, thermostats use either cycle per hour (CPH) control or deadband control to meet this user expectation. CPH control sets a number of times (cycles) that the HVAC system is turned on within one hour. One disadvantage to CPH control is that although it will typically provide an average temperature near the set point, the sensed temperature may sometimes overshoot the set point by more than 1° F. (0.5° C.). Alternatively, deadband control simply turns the HVAC system ON or OFF based on a comparison of the sensed temperature to a predetermined temperature below the temperature set point and a predetermined temperature above the temperature set point. Deadband control, particularly for multi-stage HVAC systems, can result in the output temperature shifting away from the temperature set point. Therefore, overshooting the temperature set point and set point shifting are common problems associated with the alternative control systems of the known thermostats.